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Recent Hominin Cranial Form and Function Ricardo Miguel Alves Correia Godinho Phd in Human Sciences the University of Hull and T

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Recent Hominin Cranial Form and Function Ricardo Miguel Alves Correia Godinho Phd in Human Sciences the University of Hull and T Recent Hominin Cranial Form and Function Ricardo Miguel Alves Correia Godinho PhD in Human Sciences The University of Hull and The University of York Hull York Medical School June 2016 Abstract This thesis aims to assess if biting mechanics drives craniofacial morphology in recent hominins. To that end, a virtual functional morphology toolkit, that includes Finite Element Analysis (FEA) and Geometric Morphometrics (GM), is used to simulate biting, measure bite force and quantify deformations arising due to simulated biting in Homo sapiens and its proposed ancestral species, Homo heidelbergensis. Moreover, the mechanical significance of the frontal sinus and of the brow-ridge is also assessed in Kabwe 1 (a Homo heidelbergensis specimen). The frontal sinus is examined by comparing the mechanical performance in three FE models with varying sinus morphology. A similar approach is applied to the brow-ridge study. This approach relies on the assumption that FEA approximates reality. Thus, a validation study compares the deformations experienced by a real cranium under experimental loading with those experienced by an FE model under equivalent virtual loading to verify this assumption. A sensitivity analysis examines how simplifications in segmentation impact on FEA results. Lastly, the virtual reconstruction of Kabwe 1 is described. Results show that prediction of absolute strain magnitudes is not precise, but the distribution of regions of larger and smaller (i.e. pattern of) deformations experienced by the real cranium is reasonably approximated by FEA, despite discrepancies in the alveolus. Simplification of segmentation stiffens the model but has no impact on the pattern of deformations, with the exception of the alveolus. Comparison of the biting performance of Kabwe 1 and H. sapiens suggests that morphological differences between the two species are likely not driven by selection of the masticatory system. Frontal sinus morphogenesis and morphology are possibly impacted by biting mechanics in the sense that very low strains are experienced by this region. Because bone adapts to strains, the frontal sinus is possibly impacted by this mechanism. Lastly, biting mechanics has limited impact on brow-ridge morphology and does not explain fully the enormous brow-ridge of Kabwe 1. Hence, other explanations are necessary to explain this prominent feature. Table of Contents Abstract ................................................................................................................ 2 Table of Contents ................................................................................................. 3 List of Figures ...................................................................................................... 7 List of Tables ...................................................................................................... 12 Acknowledgements ............................................................................................ 13 Author's declaration............................................................................................ 14 1 Introduction ................................................................................................ 15 1.1 Introduction ........................................................................................ 16 1.2 Bone biomechanical function and adaptation .................................... 19 1.2.1 Bone structure ................................................................................ 19 1.2.2 Bone mechanical properties ........................................................... 21 1.2.3 Bone mechanical adaptation .......................................................... 25 1.3 Cranial form and function .................................................................. 28 1.3.1 Production of bite force .................................................................. 28 1.3.2 Resisting biting .............................................................................. 29 1.3.3 Cranial form, function, modularity, integration and equifinality ... 32 1.4 Cranial form in Homo heidelbergensis and Homo sapiens ................ 34 1.4.1 Homo heidelbergensis .................................................................... 34 1.4.2 Homo sapiens ................................................................................. 36 1.5 Measuring cranial form and mechanical function .............................. 38 1.5.1 Morphometrics ............................................................................... 39 1.5.1.1 Geometric Morphometrics ....................................................... 40 1.5.1.1.1 Landmarking ..................................................................... 40 1.5.1.1.2 Registration ....................................................................... 41 1.5.1.1.3 Analysis ............................................................................ 42 1.5.1.1.3.1 Visualising differences in size and shape .................. 43 Recent hominin cranial form and function | 4 1.5.2 Quantifying masticatory system mechanical function ................... 44 1.5.2.1 Finite Element Analysis ........................................................... 45 1.5.2.1.1 Pre-processing .................................................................. 45 1.5.2.1.1.1 Model creation ........................................................... 45 1.5.2.1.1.2 Material Properties .................................................... 46 1.5.2.1.1.3 Boundary conditions .................................................. 47 1.5.2.1.2 Solution and post-processing ............................................ 48 1.5.2.1.3 Validation and sensitivity analysis ................................... 48 2 Validation study of a voxel-based finite element model of a cadaveric human cranium approximating a molar bite .................................................................. 50 2.1 Introduction ........................................................................................ 51 2.2 Materials and Methods ....................................................................... 54 2.2.1 In vitro experiment ......................................................................... 54 2.2.2 FE experiment ................................................................................ 56 2.2.3 In vitro vs. FE experiment .............................................................. 58 2.3 Results ................................................................................................ 59 2.3.1 In vitro experiment ......................................................................... 60 2.3.2 Predicted strains ............................................................................. 64 2.3.3 Real vs Predicted Strains ................................................................ 68 2.4 Discussion .......................................................................................... 74 3 Sensitivity analysis of a voxel-based finite element model of a cadaveric human cranium ............................................................................................................... 80 3.1 Introduction ........................................................................................ 81 3.2 Materials and Methods ....................................................................... 84 3.3 Results ................................................................................................ 87 3.4 Discussion .......................................................................................... 91 4 Virtual reconstruction of Kabwe 1 ............................................................. 95 4.1 Introduction ........................................................................................ 96 4.2 Materials and Methods ....................................................................... 98 4.3 Results and discussion ..................................................................... 101 5 The biting performance of H. heidelbergensis and H. sapiens ................ 106 Recent hominin cranial form and function | 5 5.1 Introduction ...................................................................................... 107 5.2 Materials and Methods ..................................................................... 110 5.2.1 Finite Element Models ................................................................. 111 5.2.1.1 Skull reconstruction and model creation ............................... 112 5.2.1.1.1 Kabwe 1 .......................................................................... 112 5.2.1.1.2 Homo sapiens ................................................................. 112 5.2.1.2 Constraints ............................................................................. 113 5.2.1.3 Material properties ................................................................. 113 5.2.1.4 Muscle loads .......................................................................... 114 5.2.1.5 Model solution, analysis and scaling ..................................... 115 5.3 Results .............................................................................................. 118 5.3.1 Mechanical advantages ................................................................ 118 5.3.2 Bite forces and force production efficiency ................................. 119 5.3.3 Strains ........................................................................................... 122 5.3.4 Magnitudes and modes of global
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